Data volume is increasing every day, and a large amount of information is stored into storage devices. As block storage, such storage has appeared that logical disks are configured by hierarchically configuring physical disks with different performances, frequently accessed data are placed on a nonvolatile memory and less frequently accessed data are placed on a low-speed disk to be able to respond with a close level of performance to a nonvolatile memory at less cost. The abovementioned performance is access response performance (access speed). Further, there is a technique which compresses identical data held by a plurality of users and backup data by using the deduplication technique. Furthermore, a service provided with a function of CAS (Content Addressable Storage) as a cloud storage service has become general.
Also, such a storage system has been proposed that combines block storage and object storage to be able to store data of amount exceeding the specifications of a storage device included by the block storage. Object storage is a kind of storage which manages data by data units called objects. Object storage allows access to an object based on information unique to the object without designation of a directory in a hierarchical directory structure. An example of such block storage and storage systems is disclosed in Patent Document 1.
Block storage disclosed in Patent Document 1 collects a predetermined number of blocks with lower access frequency than a threshold, transmits the blocks to object storage, and deletes the transmitted blocks from the block storage.
Further, following techniques are proposed in relation to the present invention.
Patent Document 2 discloses a system which is composed of a server and a plurality of storage and performs data deduplication. Patent Document 2 also discloses calculating data access frequency, regularly moving data with low access frequency to a lower hierarchy, and moving data with low access frequency to other storage.
Patent Document 3 discloses a storing backup image of data stored in an auxiliary storage device of an information processing device, into an external device connected to the information processing device.
Patent Document 4 discloses a technique which, under an environment including a single storage subsystem and a plurality of deduplication storage devices connected to the storage subsystem, prevents the same data from being stored into different deduplication storage devices.
Patent Document 5 discloses a technique including a server and an online storage service and storing data deduplicated on the server into the online storage service.    Patent Document 1: Japanese Unexamined Patent Application Publication No. JP-A 2015-179422    Patent Document 2: Japanese Unexamined Patent Application Publication No. JP-A 2013-222230    Patent Document 3: Japanese Unexamined Patent Application Publication No. JP-A 2013-137630    Patent Document 4: Japanese Unexamined Patent Application Publication No. JP-A 2013-047933    Patent Document 5: Japanese Unexamined Patent Application Publication No. JP-A 2012-141739    Patent Document 6: Japanese Unexamined Patent Application Publication No. JP-A 2012-063902
According to the technique disclosed in Patent Document 1, by combining block storage with object storage, a storage system which can store data of amount exceeding the specifications of a storage device included by the block storage can be realized. However, it has a problem that in a case where a plurality of block storage share single object storage, if the object storage does not have the deduplication function, the same data from the plurality of block storage are duplicated and stored into the object storage.